Atrial fibrillation (AF) is a form of cardiac arrhythmia characterized by rapid randomized contractions of atrial myocardium, causing an irregular, often rapid ventricular rate. The regular pumping function of the atria is replaced by a disorganized, ineffective quivering. Atrial fibrillation is caused, in large part, by chaotic conduction of electrical signals through the upper chambers of the heart. Atrial fibrillation is often associated with other forms of cardiovascular disease, including congestive heart failure, rheumatic heart disease, coronary artery disease, left ventricular hypertrophy, cardiomyopathy or hypertension.
Various techniques have been proposed for the treatment of atrial fibrillation by blocking errant electrical signal conduction in the heart. For example, the “Maze procedure” was developed in the early 1990s to treat atrial fibrillation by forming a series of physical incisions (in the form of a maze) to create scar tissue in the heart that would stop or redirect the electrical impulses. Although these procedures were originally performed with a scalpel, various other techniques have also been developed to form lesions.
Researchers have come to realize that the origins of AF often lie in the left atrium in the vicinity of the pulmonary veins. A lesion encircling the pulmonary veins is currently considered to be one of the most important areas to isolate. Additionally, a second lesion extending from the pulmonary veins to the mitral valve annulus is also considered advantageous. This mitral valve annulus lesion is sometimes referred to as the “left isthmus block.”
Typically, such lesions are formed from within the heart (by applying a scalpel or other ablation instrument to the endocardial tissue). In fact, it is becoming increasingly commonplace for patients undergoing open heart cardiac surgery (e.g., for mitral valve replacement) to also have an ablative procedure if they have a history of AF.
These procedures are very invasive (requiring a sternotomy, cardiopulmonary bypass, cardioplegic arrest, and cardiac incisions) to enter the left atrium of the heart and create the lesions. Despite various advances in rapid lesion-forming devices (such as ultrasound, radio-frequency (RF), laser and cryogenic instruments), open heart surgery has a significant morbidity and remains a procedure of last resort for treating AF except when other conditions mandate such surgery.
Considerable effort has been made to find ways to treat atrial fibrillation without cardiac arrest and open-heart surgery. For example, light based systems for creating lesions on the outer surface of the heart have been disclosed in U.S. Pat. No. 6,558,375 entitled “Surgical Ablation Instruments for Forming an Encircling Lesion” herein incorporated by reference in its entirety. In such systems, radiant energy is applied to the epicardium to induce a transmural lesion. These systems permit the surgeon to encircle the pulmonary veins with an instrument and create a lesion by photoablation. Others have proposed similar epicardial devices based on ultrasound and the like. Such systems avoid the need to stop the heart (cardioplegic arrest).
Although epicardial ablation devices have been proposed to create lesions around the pulmonary veins, access to the regions of the atrium extending from the pulmonary veins to the mitral valve annulus remains a problem, primarily because other cardiac structures can preclude epicardial access. In particular, the coronary sinus and circumflex artery lie directly above the target region for creation of the left isthmus block or lesion. If ablative energy is applied to the circumflex coronary artery in an effort to form an atrial lesion, stenosis of this blood vessel can occur and potentially result in a myocardial infarction or even death.
Thus, there exists a need for better ablation instruments and techniques. In particular, instruments capable of forming lesions extending from the pulmonary veins to the mitral valve annulus would satisfy an important need in the field.